Pay per click (“PPC”) is an Internet advertising model used to direct traffic to advertisers' websites. Based on such a model, webpage publishers display clickable advertisements in exchange for a fee from advertisers when a user clicks on the displayed advertisements. Often, an advertising network (e.g., Microsoft AdCenter®) can act as an intermediary between advertisers and publishers. The advertising network charges an advertiser for a click on its advertisement and pays the publisher who displays the advertisement.
One problem with PPC advertising is click fraud. Click fraud generally refers to the practice of a person (or a computer program) imitates a legitimate user's clicking on an advertisement for generating a charge per click without having actual interest in a target of the advertisement. Click fraud can be committed under different situations. For example, a publisher may commit click fraud by clicking on advertisements displayed on his/her own webpages to increase fees collected from an advertiser or advertising network. In another situation, a person or business may commit click fraud by repeatedly clicking on a competitor's advertisements with the intent of exhausting the competitor's advertising budget. Even though various detection and prevention techniques have been developed, click fraud remains a serious problem.